Pluripotent stem cells, such as, for example, embryonic stem cells have the ability to differentiate into all adult cell types. As such, embryonic stem cells may be a source of replacement cells and tissue for organs that have been damaged as a result of disease, infection, or congenital abnormalities. The potential for embryonic stem cells to be employed as a replacement cell source is hampered by the difficulty of propagating the cells in vitro while maintaining their pluripotency.
Current methods of culturing undifferentiated embryonic stem cells require complex culture conditions, such as, for example, culturing the embryonic stem cells in the presence of a feeder cell layer. Alternatively, media obtained by exposure to feeder cell cultures may be used to culture embryonic stem cells. Culture systems that employ these methods often use cells obtained from a different species than that of the stem cells being cultivated (xenogeneic cells). Additionally, these culture systems may be supplemented with animal serum.
Embryonic stem cells provide a potential resource for research and drug screening. At present, large-scale culturing of human embryonic stem cell lines is problematic and provides substantial challenges. Current in vitro methods to propagate pluripotent stem cells are carried out in tissue flasks on planar surfaces pre-coated with extracellular matrix (ECM) proteins or feeder cells. Planar cultures also require frequent subculturing because their limited surface area cannot support long-term growth of pluripotent stem cells. Micro-carrier-based methods of pluripotent stem cell culture may provide a solution. Micro-carriers have a high surface-area-to-volume ratio and, therefore, eliminate the surface area restriction of growing pluripotent stem cells on planar surfaces.
For example, Fok et at disclose stirred-suspension culture systems for the propagation of undifferentiated ESC—micro-carrier and aggregate cultures (Stem Cells 2005; 23:1333-1342.)
In another example, Abranches et at disclose the testing of Cytodex 3® (GE Healthcare Life Sciences, NJ), a microporous micro-carrier made up of a dextran matrix with a collagen layer at the surface for its ability to support the expansion of the mouse S25 ES cell line in spinner flasks (Biotechnol. Bioeng. 96 (2007), pp. 1211-1221.)
In another example, US20070264713 disclose a process for cultivating undifferentiated stem cells in suspension and in particular to a method for cultivating stem cells on micro-carriers in vessels.
In another example, WO2006137787 disclose a screening tool is used which comprises particulate matter or micro-carriers, such as beads, attached to a solid support, such as a micro titer plate, for the cultivation of cells on said micro-carriers.
In another example, WO2008004990 disclose a method of promoting the attachment, survival and/or proliferation of a stem cell in culture, the method comprising culturing a stem cell on a positively-charged support surface.
In another example, WO2007012144 disclose a bioreactor, comprising: a support surface; and a synthetic attachment polypeptide bound to the support surface wherein the synthetic attachment polypeptide is characterized by a high binding affinity for an embryonic stem cell or a multipotent cell.